Don't underestimate how much grief you will get from clients paying pennies. it is a FACT in business, that those that pay the least expect the most, it is their nature and has been proven time and time again.
We had a system like this that offered FREE space to people, so they were not paying a penny. We only offered email support with a 24 hour turnaround (as it was free). I had people track me down via the web (as there were links on the site to our main business which needed to be there by law), and telephone me anyhow DEMANDING i help them there and then!
We scrapped it within months of it going live. I was using an out of the box system that was so simple to use my 9 yr old could use it.
It isn't the case of frequent changes, it is a case of some people wanting to make changes and breaking it, then getting in touch.
I wish you luck with this though, I hope you make a good go of it
